The present invention relates to thermal and stress mapping of a body lumen, and more particularly to analyzing the material strain and color of the surface of a lesion molding balloon to classify the type of lesion and whether it is vulnerable to rupture.
It is widely recognized that plaques or lesions can be classified into three broad categories: calcified or hard plaque lesions, fibrous or soft lesions and inflamed soft lipid filled plaques or lesions. The diagnosis of the type of lesion drives the particular treatment of the lesion, whether it is removal of the lesion by rotablator, predilatation by balloon angioplasty, delivery of a stent, with or without predilatation, or the like.
In particular, the identification of inflamed plaques or lesions is important since these lesions are at greatest risk of rupture, which can lead to a large thrombus or blood clot, which can completely occlude the flow of blood through the artery, leading to injury of the heart or brain. An inflamed or vulnerable lesion is characterized by its cap thickness, lipid pool size and inflammation or temperature. This is discussed in great detail in WO 97/10748 published Mar. 27, 1997 and entitled xe2x80x9cDetecting Thermal Discrepancies In Vessel Wallsxe2x80x9d, the entire contents of which are hereby incorporated by reference. As discussed in the published PCT application, considerable evidence indicates that plaque rupture triggers 60-70% of fatal myocardial infarctions. As is well known in the art, and described in the published PCT application, an inflamed plaque is hotter than the surrounding tissue. This published PCT patent application relates to using an infrared fiberoptic system to locate inflamed heat producing plaque. However, the device described in this PCT published application is very expensive, making it available in a limited number of procedures. What is needed is a more inexpensive method for classifying plaques or lesions, and in particular determining which plaques are hard, soft or inflamed, which drives the treatment after diagnosis.
Applicants have discovered that in addition to providing a three-dimensional (3D) image of the geometry of a lesion or plaque in a body lumen, the balloon can be further analyzed to determine its material stress, which can in turn be used to determine the temperature of a lesion as well as the hardness of a plaque or lesion. Differences between the observed material stress and a baseline material stress can also determine temperature differences along the balloon surface, which can be used to aid in determining whether a particular lesion is inflamed and vulnerable to rupture. The material stress of the balloon material manifests itself in the color pattern observed under white light with a polariscope.
The inventive method requires advancing a three-dimensional imaging balloon catheter to the site of a lesion to be imaged, inflating or molding the balloon to image the lesion, deflating the balloon, withdrawing the catheter from the body lumen and re-inflating the balloon which reassumes its memorized shape. Stress mapping of the balloon is then done by analyzing the material strain and color of the re-inflated 3D imaging balloon.
Direct observation of the color pattern which is predominantly blue/green is considered indicative of an inflamed lesion. More precise temperature mapping may be performed by digitizing the surface geometry of the balloon and computing the color pattern based on the digitized surface geometry and the observed narrowest balloon diameter IDi. By comparing the differences between a computed color pattern, which is based on the digitized surface geometry of the balloon, to the observed color pattern, a temperature map can be generated which can be used to determine whether a lesion is an inflamed vulnerable lesion which is at greatest risk of rupture. The color pattern may also be used to determine whether the lesion is a hard calcified lesion.
The comparison of color patterns may be done with a flip-chart of baseline images or by using a computer to match the actual color pattern to a baseline image.
In addition to using a polariscope and analyzing the color patterns, an alternate embodiment of the inventive step would utilize a temperature sensitive balloon material which would change color depending on the temperature of the body lumen, which could vary along its axial length. Using such a temperature sensitive balloon material would allow direct observation of the withdrawn balloon which would provide a temperature map of the body lumen including a lesion, which would then indicate directly whether the lesion was inflamed by observing whether the temperature was higher than the normal body temperature.